Wouldn’t it be easier for doctors if our skin was transparent and they could see everything beyond or beneath it? Sounds fantastical, right? Even with advanced technologies and highly sophisticated imaging techniques, doctors get ambiguous results when they peer inside a living body. However, recent research has shown that this distant dream could soon be a reality, surprisingly, just by applying a common food colouring.
Researchers at Stanford University have successfully peered inside the bodies of living animals using common food colouring, temporarily turning their skin, muscles and connective tissue transparent, The Guardian reports.
The research, published in Science on September 5, describes how rubbing an FDA-approved dye solution on mice’s skin allowed researchers to see through the skin without making an incision. They were able to do so with the naked eye.
After applying the dye to the abdomen, the rat’s liver, intestines and bladder became visible through the abdominal skin. Not only this, the researchers also saw the blood vessels in the rat’s brain.
Interestingly, the treated skin color returned to normal after the researchers washed off the dye.
“As soon as we rinsed the skin with water and massaged, the effect was reversed within a few minutes. This is an amazing result,” said Guosong Hong, assistant professor of materials science and engineering.
How does this work?
The idea behind it echoes the approach of a character in the popular 1897 novel, The Invisible Man. In the science fiction novel written by H.G. Wells, a scientist discovers that the secret of invisibility depends on matching the object’s refractive index – or ability to bend light – with the surrounding air.
When light waves strike biological tissue, it scatters them, making it appear opaque and non-transparent to the eye. This effect is caused by differences in the refractive index of different tissue components, such as lipids and water. In the visible spectrum, water generally has a lower refractive index than lipids. This causes visible light to scatter while it passes through tissue containing both.
The researchers massaged a solution of red tartrazine onto the abdomen, scalp and hind legs of unconscious mice to match the refractive indices of different tissue components.
Soon after, the rodent’s skin turned red, indicating that most of the blue light was absorbed due to the presence of the light-absorbing molecule, the study said.
The increase in absorption further changed the refractive index of water at different wavelengths – which was red in this case. As a result, the refractive index of water matched the refractive index of lipids in the red spectrum. Ultimately, this reduced scattering and made the rat skin appear more transparent at red wavelengths.